1. Field of the Invention
The present invention relates to a rotary type stencil printing machine. According to the rotary type stencil printing machine of the present invention, a print sheet is printed while being carried by being sandwiched between a printing drum and a back press roller. Further, the print sheet is carried while being pressed to the back press roller by a pinch roller after having been peeled off from the printing drum.
2. Description of the Related Art
FIG. 15 is a sectional view showing an example of a basic structure of a conventional rotary type stencil printing machine.
The stencil printing machine is provided with a printing drum 100. The printing drum 100 is provided with a base member 103 comprising a pair of circular plate members 101 arranged coaxially on a common central axis line 104 and a stencil clamping base 102 for connecting the pair of circular plate members 101. The base member 103 is fixed with a gear, not illustrated, coaxially with the central axis line 104. The gear is in mesh with a drive gear, not illustrated. By rotation of the drive gear, the base member 103 is driven to rotate centering on the central axis line 104.
A screen member 105 which is ink-permeable and flexible, is made to wrap on the base member 103. One end portion of the screen member 105 is fixed to the stencil clamping base 102 of the base member 103. The screen member 105 is made to wrap on outer peripheral surfaces of the circular plate members 101. Other end portion of the screen member 105 is elastically attached to the stencil clamping base 102 via a spring, not illustrated. Therefore, the screen member 105 is elastically deformed outwardly when depressed from an inner side thereof. The stencil clamping base 102 is provided with clamping means 107. Perforated stencil sheet 106 is fixed to the stencil clamping base 102 at a front side thereof by the clamping means 107 and is made to wrap on an outer circumferential surface of the screen member 105.
At an inner portion of the printing drum 100, a squeegee roller 110 is vertically movably provided. The squeegee roller 110 is lifted and lowered at a predetermined timing in synchronism with rotation of the printing drum 100 and presses the screen member 105 outwardly. Ink supplying means, not illustrated, supplies a constant amount of ink onto a peripheral face of the squeegee roller 110.
On a lower side of the printing drum 100, a press drum 200 which is a back press roller is arranged. A diameter of the press drum 200 is substantially the same as that of the printing drum 100. A rotational axis line 201 of the press drum 200 and the central axis line 104 of the printing drum 100 are in parallel with each other. In a nonprinting state, a very small clearance is provided between the printing drum 100 and the press drum 200. The press drum 200 is driven to rotate in a direction reverse to that of the printing drum 100 in synchronism with rotation of the printing drum 100.
A recess portion 202 is formed at an outer circumferential surface of the press drum 200. When the printing drum 100 and the press drum 200 are rotated in synchronism with each other, the recess portion 202 corresponds to the clamping means 107 of the printing drum 100. Therefore, even when a clearance between the printing drum 100 and the press drum 200 is very small, the clamping means 107 does not collide with the press drum 200.
A clamp 203 is provided at proximity of the recess portion 202 of the press drum 200. The clamp 203 holds a front end of print sheet supplied between the printing drum 100 and the press drum 200. The print sheet is held by the clamp 203, thereafter, sandwiched between the press drum 200 and printing drum 100 in accordance with rotation of the press drum 200 and is fed forwardly.
At proximity of the press drum 200, a pinch roller 300 is rotatably provided. The pinch roller 300 is arranged side by side on a sheet discharge side of the press drum 200. The pinch roller 300 presses the print sheet immediately after having been printed to the press drum 200 and peels off the print sheet from the printing drum 100. Two pieces of the pinch rollers 300 are brought into contact with two edge portions in the width direction of the print sheet. A clearance between the two pieces of pinch rollers 300 in the axial direction can be adjusted in accordance with a width of the print sheet.
The print sheet is supplied between the printing drum 100 and the press drum 200. The squeegee roller 110 is lowered and presses the screen member 105 outwardly at the predetermined timing. The screen member 105 and stencil sheet 106 which are deformed outwardly, sandwich the print sheet between the press drum 200 and the screen member 105 and stencil sheet 106. The print sheet is carried while being sandwiched between the deformed printing drum 100 and the press drum 200. While the print sheet is being carried, ink supplied to an inner circumferential face of the screen member 105, passes through the screen member 105 and stencil sheet 106, is transcribed onto the print sheet and forms an image.
When the stencil printing machine is brought into a standby state, the printing drum 100 and the press drum 200 are brought into a positional relationship shown by FIG. 15. That is, the clamping means 107 of the printing drum 100 and the recess portion 202 of the press drum 200 coincide with each other. Therefore, the pinch roller 300 is brought into contact with the outer circumferential surface of the press drum 200. Under the state, the two pieces of pinch rollers 300 can not be moved in the axial direction in accordance with the width of the print sheet. In order to move the pinch rollers 300 in the axial direction, it is necessary to rotate the press drum 200 to a pinch roller moving position shown in FIG. 16 and coincide the recess portion 202 of the press drum 200 with the pinch rollers 300 to thereby enable to move the pinch rollers 300 without resistance.
As has been explained above, according to the conventional stencil printing machine, a time period for moving the press drum 200 is needed for adjusting positions of the pinch rollers 300. The time period for moving the press drum 200 is added to first print time and start up time for printing. The first print time indicates a time period from when a print button is depressed until a sheet of printed matter is discharged. It is generally recognized that the shorter the time period the higher the function of the printing machine and shortening of the first print time has been desired.
It is an object of the present invention to provide a rotary type stencil printing machine having short first print time since positions of pinch rollers can be adjusted without rotating a press drum.
According to a first aspect of the present invention, there is provided a rotary type stencil printing machine comprising a printing drum (2) on which a perforated stencil sheet is made to wrap and which is rotated, a press drum (10) arranged at a vicinity of the printing drum and rotated in a direction reverse to a direction of the printing drum, pinch rollers (15) rotatably provided at a vicinity of the press drum for pressing a print sheet to the press drum such that the print sheet, which has been sandwiched between the printing drum and the press drum and printed, is held and carried by the press drum, pinch roller position adjusting means for adjusting positions of the pinch rollers in an axis line direction such that the pinch rollers can be brought into contact with predetermined positions of the print sheet, pinch roller releasing means for moving the pinch rollers between pinch positions at which the pinch rollers are brought into contact with the press drum and release positions at which the pinch rollers are separated from the press drum and controlling means (40) for controlling the pinch roller position adjusting means and the pinch roller releasing means such that the positions of the pinch rollers in the axis line direction can be adjusted only when the pinch rollers are set to the positions separated from the press drum.
According to a second aspect of the present invention, there is provided the rotary type stencil printing machine according to the first aspect, further comprising a sheet width sensor (17) for detecting a width of the supplied print sheet, wherein the pinch rollers (15) are two pieces of pinch rollers for pressing two edge portions of the print sheet in a width direction to the press drum, the pinch roller position adjusting means comprising a pair of moving members (20) made movable in the width direction of the print sheet and attached with the pinch rollers, moving means (belt 23) for moving the pair of moving members in directions reverse to each other and a movement detecting sensor (movement sensor 26) for detecting positions of the moving members, the pinch roller releasing means comprising attaching means (arms 30) for attaching the pinch rollers pivotably to the moving members, driving means (release motor 35) for setting the pinch rollers to the release positions or the pinch positions by pivotably moving the pinch rollers relative to the moving members and a release detecting sensor (release sensor 37) for detecting whether the pinch rollers are brought into a release state and the controlling means (40) sets the pinch rollers to the release positions by operating the driving means of the pinch roller releasing means after finishing a printing operation and controls the pinch roller position adjusting means in accordance with a signal from the sheet width sensor before carrying out the printing operation.
According to a third aspect of the present invention, there is provided the rotary type stencil printing machine according to the second aspect, wherein the pinch roller releasing means further comprises cams (release cams 36), which are connected to the driving means and pivoting, and an operating plate (32), which is provided to be brought into contact with the cams and pivoted by pivoting the cams and one end portion of which is engaged with the attaching means, and the pinch rollers are moved by the driving means, the cams, the operating plate and the attaching means.
According to a fourth aspect of the present invention, there is provided the rotary type stencil printing machine according to the second aspect, wherein the pinch roller releasing means further comprises cams (release cams 36), which are connected to the driving means and pivoting, an operating plate (32), which is provided to be brought into contact with the cams and pivoted by pivoting the cams and one end portion of which is engaged with the attaching means (arms 30), returning means (spring 50) for urging the operating plate in a release direction and an elastic member (torsional coil spring 51) having one end portion locked to the attaching means and the other end portion pressed by the operating plate moved in a pinch direction reverse to the release direction. According to the constitution, when the cams move the operating plate in the pinch direction against the returning means, the operating plate moves the attaching means in the pinch direction via the elastic member and sets the pinch rollers to the pinch positions. Further, when the cams permit the operating plate to move in the release direction by the returning means, the operating plate moves the attaching means in the release direction and sets the pinch rollers at the release positions.
According to a fifth aspect of the present invention, there is provided a rotary type stencil printing machine comprising, a printing drum (2) on which perforated stencil sheet is made to wrap and which is rotated, a press drum (10) arranged at a vicinity of the printing drum and rotated in a direction reverse to a direction of the printing drum, a paper discharge roll (61) arranged at a vicinity of the press drum and rotated in a direction the same as a direction of the press drum, pinch roller pairs (65) provided respectively rotatably at vicinities of the press drum and the paper discharge roll for pressing print sheet to the press drum and the paper discharge roll such that the print sheet which has been sandwiched between the printing drum and the press drum and printed is held and carried by the press drum and the paper discharge roll, pinch roller position adjusting means for adjusting positions of the pinch roller pairs in an axis line direction such that the pinch roller pairs can be brought into contact with predetermined positions of the print sheet, pinch roller releasing means for moving the pinch roller pairs between pinch positions at which the pinch roller pairs are brought into contact with the press drum and the paper discharge roll and release positions at which the pinch roller pairs are separated from the press drum and the paper discharge roll and controlling means (40) for controlling the pinch roller position adjusting means and the pinch roller releasing means such that the positions of the pinch rollers in the axis line direction are adjusted only when the pinch roller pairs are set to the positions separated from the press drum and the paper discharge roll.
According to a sixth aspect of the present invention, there is provided the rotary type stencil printing machine according to the fifth aspect, further comprising a sheet width sensor (17) for detecting a width of the supplied print sheet, wherein the pinch roller pairs (65) are two sets of pinch roller pairs for pressing two edge portions of the print sheet in a width direction to the press drum, the pinch roller position adjusting means comprising a pair of moving members (68) made movable in the width direction of the print sheet and respectively attached with the two sets of pinch roller pairs, moving means (69) for moving the pair of moving members in directions reverse to each other and a movement detecting sensor (26) for detecting positions of the moving members, the pinch roller releasing means comprising driving means (87) for setting the pinch roller pairs to the release positions or the pinch positions, cams (83) driven to rotate by the driving means, an operating member (70) provided to be brought into contact with the cams, pivoted by pivoting the cams and provided with the pair of moving members via the moving means and a release detecting sensor (37) for detecting whether the pinch roller pairs are brought into a release state and wherein the controlling means (40) sets the pinch roller pairs to the release positions by operating the driving means of the pinch roller releasing means after finishing a printing operation and controls the pinch roller position adjusting means in accordance with a signal from the sheet width sensor before carrying out the printing operation.